Regardless of calendars and clocks, we all experience endless workdays and vacation weeks that fly by; insufferable minutes of boredom and three-hour movies that end without us noticing. It is an unquestionable psychological phenomenon, but until now the specific biological springs that produced it were unknown.
Researchers at the Champalimaud Center for the Unknown, in Lisbon, have just published in the journal Science the results of an experiment with mice that identifies neurons associated with the subjective sensation of the passage of time. For some years, this team of scientists studied the way in which the human brain connected causes with effects over time, but an experience of the main researcher, Joe Paton, focused his interest on the subjective perception of duration. Some friends of Paton had an accident, and the hours that elapsed between the moment he learned of the event and they told him that the victims were well were for him weeks. Why?
Paton and his colleagues narrowed down a very specific area of exploration: a deep structure called the substantia nigra , in the midbrain. Their neurons secrete the neurotransmitter dopamine, a substance generally associated with motivation, pleasure and desire, but which also has to do with temporal estimation : Parkinson’s, which destroys the substantia nigra, affects this capacity. In addition, its neurons connect with another area, the striatum , also related to the subjective sensation of time.
The experiment consisted of training the mice to, for example, estimate whether the duration between two tones was greater or less than 1.5 seconds and simultaneously measure the activity of dopamine-producing neurons using highly advanced molecular tools. When they got it right, the rodents received a reward.
Control neuronal
Thus, they observed not only that the nerve cells of the substantia nigra were effectively involved in the task, but also that they fired at different levels of intensity following a pattern : the higher the electrical activity, the more likely the mice were to underestimate the power. The duration of the interval, and the less their neurons worked, the longer it became.
The neurons seemed to reflect information about time estimation, but do they also control that perception? To verify this, the scientists used a neural manipulation technique called optogenetics, using pulses of light, and the result was positive: when they stimulated the activity, the mice were shortened, and vice versa .
The problem is that we cannot know what laboratory animals feel (we do not have their testimony, obviously), and it is difficult to extrapolate to humans , but the researchers believe that similar mechanisms must be involved in our case.
